Explain Binding Mode In WPF

Binding is the main feature of the WPF. For understanding binding, we take two controls - Source control and Target control. WPF has four types of binding modes -

• One Way
• Two Way
• One Way to source
• One Time

Here, for understanding these all bindings, let's take one example. Make one WPF application which has two controls - slider and textbox, as shown below. 

<Grid>
        <StackPanel Orientation="Vertical">
            <Slider Name="mySlider" Maximum="100" Minimum="0" Margin="20"></Slider>
            <TextBox Name="txtValue" Margin="20" Width="50" Height="30"></TextBox>
        </StackPanel>
</Grid>

Output



Now, let's learn all the bindings, one by one. 

• One Way
  
  In One Way binding, source control updates the target control, which  means if you change the value of the source control, it will update the value of the target control. So, in our example, if we change the value of the slider control, it will update the textbox value, as shown below.
  

  <TextBox Name="txtValue" Text="{Binding ElementName=mySlider, Path=Value, Mode=OneWay}"
               Margin="20" Width="50"
               Height="30">
  </TextBox>

  Here, we use the binding property on target control and we specify the element name and path (or whatever things you want to update), and mode of binding. So, full code is.
  

  <Grid>
        <StackPanel Orientation="Vertical">
            <Slider Name="mySlider" Maximum="100" Minimum="0" Margin="20"></Slider>
            <TextBox Name="txtValue" Text="{Binding ElementName=mySlider, Path=Value, Mode=OneWay}" Margin="20" Width="50" Height="30"></TextBox>
        </StackPanel>
  </Grid>

  Now, run the application and check if you change the value of the slider (source), it will update the value in textbox. Yes it will. But, if you update the value in text box, then it will not update the slider value. So, it's called one way binding.
  
  
• Two Way
  
  In two way binding, source control updates the target control as well as the target control also updates the source control. That means if you change the value of the source control, it will update the value of the target control and if you change value of target control, it changes the value of the source control. So, in our example, if we change value of the slider control, it will update the textbox value and also vice versa is working, as shown below.
  

  <TextBox Name="txtvalue" Text="{Binding ElementName=mySlider, Path=Value, Mode=TwoWay,   UpdateSourceTrigger=PropertyChanged}"
               Margin="20" Width="50"
               Height="30">
  </TextBox>

  Here we use one more property: UpdateSourceTrigger, which is for instantly   (immediately) updating the control value. If you change the value in text box then it will directly affect the slider --  no need to press tab or any other action.
  
  Here, we use the binding property on target control and we specify the element name, path (whatever things you want to update), and mode of binding as shown in the above example. Now, run full code.
  

    <Grid>
          <StackPanel Orientation="Vertical">
  
              <Separator BorderThickness="20" BorderBrush="Black"></Separator>
              <Slider Name="mySlider3" Maximum="100" Minimum="0" Margin="20"></Slider>
              <TextBox Name="txtvalue3" Text="{Binding ElementName=mySlider3, Path=Value, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" Margin="20" Width="50" Height="30"></TextBox>
  
          </StackPanel>
  </Grid>

  Now, run the application and check if you change the value of the slider (source), whether it updates the value in textbox and also vice versa. So, it's called two way binding.
  
  
• One Way to source
  
  In One way to source binding, target control updates the source control which means if you change the value of the target control, it will update the value of the source control. It is just the opposite to One way binding. So, in our example, if we change the value of the slider control, it will update the textbox value; as shown below.
  

  <TextBox Name="txtvalue4" Text="{Binding ElementName=mySlider4, Path=Value, Mode=OneWayToSource, UpdateSourceTrigger=PropertyChanged}" Margin="20" Width="50" Height="30">
  </TextBox>

  Here, we use the binding property on target control and specify the element name, path, and mode of binding, as shown in the above example. Now, run the full code.
  

  <Grid>
        <StackPanel Orientation="Vertical">
  
            <Separator BorderThickness="20" BorderBrush="Black"></Separator>
            <Slider Name="mySlider4" Maximum="100" Minimum="0" Margin="20"></Slider>
            <TextBox Name="txtvalue4" Text="{Binding ElementName=mySlider4, Path=Value, Mode=OneWayToSource, UpdateSourceTrigger=PropertyChanged}" Margin="20" Width="50" Height="30"></TextBox>
        </StackPanel>
  </Grid>

  Now, run the application and check if you change the value of the textbox (target), whether it updates the value in slider. But, if you update the value in text box, then it will not update the slider value. So, it's called one way to source binding.
  
  
• One Time
  
  In one time binding, control value is updated only when the application is initialized. This means you cannot change the value from source to control; as for changing the value, you have to write code in code behind file, so that  you can change value from the back-end programming.
  

  txtvalue.Text = "50";
  mySlider.Value = Convert.ToInt32(txtvalue.Text);